1. Technical Field
The present invention generally relates to the linkage used to control a thumb used with a bucket on a prime mover such as an excavator. More particularly, the invention relates to a unique mounting and operating configuration for the progressive linkage of the thumb affixed to the dipper stick. Specifically, the present invention relates a thumb progressive linkage that is mounted to a dipper stick independent of the pin and linkage assembly used to control an attachment on the end of the dipper stick.
2. Background Information
An excavator is a machine that generally includes a boom that supports an extendable arm, known in the trade as a “dipper arm,” a “dipper stick,” or a “stick” onto which is attached an excavator tool—such as an excavator bucket or rake. The excavator tool is typically attached to the distal end of the dipper stick with a pivot pin. A piston cylinder assembly operating through a tool linkage assembly is used to control the excavator tool.
An excavator thumb may be used in combination with any of a variety of excavator tools. Pin on types of excavator thumbs typically connected to the distal end of the dipper stick with a pivot pin that also serves to mount the excavator tool. The pin on excavator thumb may be mounted in three control configurations including a stiff arm configuration, a direct connect configuration, and a progressive linkage configuration. The progressive linkage configuration provides a wider range of motion to the thumb than the other control configurations. The progressive linkage control configuration also locates the end of the cylinder rod away from the thumb and bucket by connecting the end of the cylinder rod to a progressive linkage that is, in turn, connected to the thumb body thus protecting the end of the cylinder rod from potential damage.
Numerous stick and bucket configurations are manufactured and sold by a wide variety of manufacturers. Each thumb linkage must be carefully designed for the specific stick linkage and bucket combination. Once a thumb linkage is designed for a specific stick, linkage, and bucket combination, the thumb linkage will not fit essentially any other stick linkage and bucket configuration. The uniqueness of the linkage design prevents the thumb linkages from being interchanged with other machines and thus increases the cost of owning a thumb with a progressive linkage. Excavator owners usually must purchase and maintain a thumb linkage for each of their machines. Another problem with existing progressive linkages is that they often of limited use when installed on short sticks (those of less than nine feet in length) because there is not sufficient room for the piston cylinder actuator. Although a shorter piston cylinder actuator may be used, the range of motion becomes limited. The industry thus desires a progressive linkage configuration that may be readily fit to a variety of bucket and stick configurations, is easy to install, has a greater range of motion, and lowers owning and operating costs.
Another problem with existing progressive thumb linkages is the installation sequence. The process includes repeated trial and error steps that can consume twelve to sixteen hours. The linkage configuration and the mounting sequence should be simple while improving the range of motion for the thumb. The method of mounting the linkage to the dipper stick and connecting the linkage to the thumb should be easy to understand and minimize the time required to install the tool to the excavator.